1. Field of the Invention
The present invention relates to a free-rotation control apparatus of a hoist and traction machine, and more particularly to a free-rotation control apparatus adapted to make it possible that a load sheave rotates freely by setting a mechanical brake of a hoist and traction machine to the inactivated state.
2. Description of Prior Art
Conventionally, for use in a hoist and traction machine there have been proposed various free-rotation control apparatus adapted to allow a load sheave to rotate freely so as to enable an operator to pull out and pull back a load chain rapidly. One of them is the following free-rotation control apparatus (refer to the Specification and the Drawings of Japanese Patent Application No. Hei 3(1991)-241372) previously proposed by the applicant of this invention. This apparatus has a stopper disposed at an axial end of its driving shaft, an operating handle interposed between the stopper and a driving member threadably mounted to the driving shaft and interlocked with driving means such as an operating lever so as to be axially movable between a steady state position in which it is near to the driving member and a free-rotation position in which it is spaced apart therefrom and to be impossible to rotate relatively with respect to the driving shaft, and a resilient pushing member interposed between the operating handle and the stopper so as to urge the handle toward the driving member. In the lever-type hoist and traction machine, when the operating handle is pulled out to the free-rotation position and is made to turn in the hoist and traction direction under such a condition that the rotation of the driving member is blocked, the driving shaft is rotated, so that the driving member threadably mounted to the driving shaft can be moved back with respect to a lining plate of a mechanical brake. When an action of the mechanical brake is released by that moving back, the free-rotation control can be carried out and the operating handle can be brought into resilient contact with the driving member by a pushing force of the resilient pushing member under that condition so as to maintain the free-rotation controlling state.
In the free-rotation control apparatus having the above-mentioned construction, since the operating handle is brought into resilient contact with the driving member by the urging force of the resilient pushing member at the time of free-rotation controlling so as to restrain a relative rotation of the driving member with respect to the driving shaft and maintain the free-rotation control, when the load chain is pulled out and pulled back under the free-rotation control, advantageously it becomes possible to enlarge an input range of a traction force applied to the load chain and to carry out the free-rotation operation without requiring any skill. Especially, however, in the lever-type hoist and traction machine, when the free-rotation control is carried out, it is required to firstly pull out the operating handle, then turn it so as to release the brake under such a condition that the rotation of the driving member is blocked, in other words, under such a condition that a reverse rotation pawl (a returning pawl) of the actuating pawl member provided in the operating lever meshes with teeth of the driving member so as to block the rotation of the driving member in the lever-type hoist and traction machine, and finally return an actuating pawl member to the neutral position. Therefore, when a novice operator carries out the free-rotation control, it is apprehended that the operator operates erroneously, for example changes over the actuating pawl member not to the returning pawl but to the forwarding pawl, reverses the operating handle and so on. Further, if such erroneous operations are carried out, of course it becomes impossible to carry out the free-rotation control appropriately, that results in confusion and inconvenience.